Dendritic cells (DC) and epithelial cells in human gastric mucosa interact closely to maintain tissue homeostasis. Cell-cell contacts between gastric DCs and epithelial cells are likely crucial for improving DC access to luminal antigens, DC conditioning by epithelial cell-derived soluble factors such as RA, and DC regulation of epithelial cell function. However, the molecular mechanisms of cell-cell contacts between DCs and the gastric epithelium remain unknown. CD103 (?E integrin) mediates adhesion of intestinal intraepithelial lymphocytes to epithelial E-cadherin and has been implicated in mediating DC-epithelial cell interactions in murine intestinal DCs, where it is widely expressed. In contrast, human gastric DCs express little surface CD103. However, human gastric and monocyte-derived DCs contain additional intracellular reservoirs of CD103 that can potentially be mobilized for interactions with E-cadherin. The central hypothesis that will be tested is that gastric DCs spontaneously establish cell contacts with gastric epithelial cells through CD103-E- cadherin interactions. The Specific Aims for this project are to (1) determine whether human gastric DCs interact with gastric epithelial cells in a novel organoid co-culture model and (2) determine whether human gastric DCs express functional levels of surface CD103 for E-cadherin engagement. The rationale for the proposed research is that a better understanding of how DCs interact with the gastric epithelium may allow us to target these interactions in order to manipulate the gastric immune response to H. pylori, which is inefficient and often detrimental. Gastric organoids are spheroid organotypic cultures that can be infected with H. pylori by microinjection. Here, gastric organoids will be co-cultured with gastric DCs, and DC-epithelial cell interactions will be monitored by live imaging. The endosomal trafficking of DC CD103 and potential triggers that may induce redistribution of CD103 to the cell surface will be investigated The proposed approach is innovative in that we are investigating the role and function of intracellular CD103 in human DCs for DC- epithelial cell crosstalk. In addition, the proposal is innovative because it is the first, to our knowledge, to leverage the gastric organoid model for co-culture studies with gastric DCs. The proposed research is significant because it will increase our understanding of immune cell interactions specific to the human gastric mucosa, which has received little investigative attention in spite the high prevalence of gastric H. pylori infection